Mössbauer studies of Fe inclusions in synthetic diamond

Mössbauer spectroscopy has been used to study the hyperfine interaction at Fe inclusions in a suite of MDAS synthetic diamonds of grain sizes in the range 25–250 μm. For the 250 μm grains a six line spectrum typical of α-Fe is obtained. With decreasing grain size the spectra reflect a rapid phase transition of the Fe inclusions from ferromagnetic to paramagnetic. A surprising result is the re-appearance of ferromagnetic structure in the spectrum of the finest grains studied. Electric quadrupole splitting in some of the spectra suggest that a small fraction of the Fe form Fe?C bonds at substitutional sites in the diamond lattice.